Method and Control Arrangement for Terminating Accidental Switch on of a Deep Fryer Apparatus Not Filled with Oil

ABSTRACT

Method and control arrangement for terminating an accidental switch on of a deep fryer apparatus when it is not filled with oil, the apparatus comprises a vessel having closed bottom and sides, and a horizontally formed electric heating element for direct contact with the oil within the vessel. At one or more points of the inner space of the vessel the temperature is measured, by which the accidental switch on state of the apparatus is detected and terminated at the same time in such a way that a derivative of the temperature measured at the one or more determined points is defined. The heating power is automatically cut off to terminate switched on state when the value of the derivative exceeds a predetermined threshold value.

BACKGROUND OF THE INVENTION

The present invention relates to a method and control arrangement forterminating an accidental switch on of a deep fryer apparatus when it isnot filled with oil, the deep fryer apparatus comprises a vessel closedat the bottom and at the sides, and a substantially horizontally formedelectric heating element being in direct contact with the oil is placedwithin the vessel. Deep fat fryer apparatuses in which the temperatureof the oil can be raised to a required level by means of an electricallyoperated heating element are often used in food industry. In the methodaccording to the invention the temperature is measured at one or moredetermined points of the inner space of the vessel of the deep fryerapparatus, and by observing the measured temperature value accidentalswitch on of the apparatus with a vessel without oil is detected andterminated at the same time.

In the field of gastronomy there are known methods in which thetemperature is continuously observed, and based on the measured valuescertain interventions in the operation are done. Patent application HU9700221 discloses a control unit for electronic control of gas-cookersand/or electric boiling plates and/or roasters, grillers and the like.The control unit has an EEPROM in which time and/or temperaturedependent characteristic curves and/or cycle times are stored and also,it is adapted to store additional control settings modified relative tothe ones stored in the EEPROM. Patent application DE 19628274 disclosesa safety device in which accidental switch on of household cookingappliances or fryers is prevented by means of a decoder and an automaticvoltage cut-off unit. The safety device is also applicable to switch offthe cooking appliance or fryer when it is left switched on by chance. Inboth cases, detection of temperature takes place directly, therefore aprompt signal for performing an automatic counter-measure can not beprovided for example when accidental switch on happens in a stateentirely different from the proper use, for instance when there is nooil filled in the deep fryer.

With known apparatuses when they are switched on by accident withouthaving oil filled in them, the temperature of the heating element andthe neighbouring parts within the apparatus increases rapidly whichusually leads to irreversible damage of the apparatus before accidentalswitch on is detected. To avoid this a temperature sensor is placed atone or more points within the apparatus. The signals of the sensor (s)are continuously observed and the filament current is cut off when thetemperature exceeds a predetermined value. However, experience showsthat only a threshold of such a value can be determined with which thedamage of the apparatus is unavoidable.

The object of the present invention is to provide an apparatus andmethod with which the filament current can be cut off at an earlierpoint of time, that is, before the apparatus without oil filled in itwould inevitably be damaged when it is switched on accidentally.

SUMMARY OF THE INVENTION

In the method according to the invention the derivative of thetemperature measured at one or more given point (s) is defined, and theheating power is automatically cut off in order to terminate a switchedon state of a deep fryer apparatus when the value of the derivativeexceeds a predetermined threshold value. The control arrangementaccording to the invention is adapted to determine the derivative of thetemperature measured at one or more given point(s), and to cut off theheating power in order to automatically terminate a switched on state ofa deep fryer apparatus when the value of the derivative exceeds apredetermined threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the invention will now be given with referenceto the accompanying drawings in which:

FIG. 1 is a diagram showing the temperature change plotted against timewhen the deep fryer apparatus is filled with oil;

FIG. 2 is a diagram showing the temperature change plotted against timewhen the deep fryer apparatus is not filled with oil; and

FIG. 3 is a diagram showing the temperature change plotted against timewhen the deep fryer apparatus is not filled with oil, and the heatingpower is cut off according to the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a diagram showing the temperature change plotted against timecan be seen in the case when the deep fryer apparatus is filled withoil. In the same dia-gram the change occurring in the power of the deepfryer apparatus (at the time of switching on and switching off) is alsorepresented, resulting in a stepped function curve having two explicitvalues. It is perceptible that temperature 1 at the bottom partin-creases at a constant velocity, while temperature 2 in the vicinityof the surface changes almost likewise. When temperature 1 at the bottompart or temperature 2 in the vicinity of the surface reaches apredetermined threshold value heating power is cut off automatically.

In FIG. 2 a diagram showing the temperature change plotted against timecan be seen in the case when the deep fryer apparatus is not filled withoil. Here, temperature 1 at the bottom part changes at a much highervelocity than temperature 2 in the vicinity of the surface. Then one ofthe two aforementioned temperatures may be com-pared to a predeterminedthreshold value and in case it exceeds the predetermined value heatingpower 4 is cut off. It is to be noted that a derivative of thetemperature rise in case of FIG. 1 or FIG. 2 can be easily obtained onthe basis of processing the measured temperature values. Thesederivative values 3 are marked in FIGS. 1 and 2. It is distinctlyvisible that the derivative value rises to a greater extent than thetemperature itself when there is no oil filled in the apparatus.Consequently, according to the invention instead of observing thetemperature the derivative value 3 of the same is observed and when thisderivative value 3 reaches a predetermined threshold value heating power4 is cut off. According to the foregoing the aforementioned temperaturemay be either temperature 1 at the bottom part or temperature 2 in thevicinity of the surface.

In FIG. 3 a diagram showing the temperature change plotted against timecan be seen when the deep fryer apparatus is not filled with oil, andthe heating power is cut off according to the method of the invention.It is perceptible that the value of the derivative 3 presented by anabrupt curve provides a more appropriate reference point for observingthe threshold value and to cut off the heating power 4 than directobservation of the temperatures, irrespective of the positioning of thetemperature sensors within the frying pan. In this way a much shorterreaction time can be achieved, consequently the fryer apparatus would bedamaged to a lesser degree. It can be seen in the figure that localoscillations occur in the value of the derivative due to the nature ofmeasuring and calculation, therefore it is practical to average themomentary value in a preceding time-interval window having apredetermined length, and the switched on state of the deep fryerapparatus is terminated automatically when the averaged value exceedsthe threshold value. In an alternative embodiment a plurality ofdifferent threshold values may be determined in accordance withtemperature sensors positioned at a plurality of determined pointswithin the vessel of the deep fryer apparatus, and the switched on stateof the apparatus may be terminated automatically when the value of thederivative of the temperature measured at any of the respective pointsexceeds the relevant threshold value.

The present invention can be suitably used with all kinds of fryingapparatuses such as potato fryers in which the frying process takesplace directly in the oil, and temperature sensors are used for controlof the frying process in any case. The application of the methodaccording to the invention is easy, since the control mechanism of theapparatus is adapted to compute the derivative (I. e. the differentialquotient by the time) on the basis of the temperature values which areavailable anyway, so there is no need for modification of the controlmechanism.

The advantage of the method according to the invention is that possibledamage of the deep fryer apparatus and also burning out of the heatingelement can be prevented.

1-6. (canceled)
 7. Method for automatically switching off power to aheating element of a deep fryer when the heating element is not immersedin oil in the deep fryer, the deep fryer comprising a vessel having aclosed bottom and sides wherein the heating element extendssubstantially horizontally within the vessel for direct contact with theoil, the method comprising continuously measuring temperature of theheating element at least one predetermined point on the heating element,continuously determining a derivative of the continuously measuredtemperature and automatically terminating power to the heating elementwhen the derivative exceeds a predetermined threshold.
 8. Methodaccording to claim 7, further comprising determining an average of aderivative in a time interval window immediately preceding a moment whenit is to be determined whether the power to the heating element is to beterminated and wherein the predetermined threshold of the derivative isa threshold of said average.
 9. Method according to claim 7, whereinsaid at least one predetermined point comprises a plurality ofpredetermined points, the temperature of the heating element is measuredcontinuously at each of the predetermined points, the respectivederivative of the continuously measured temperature at each of therespective predetermined points is determined and power to the heatingelement is automatically terminated when the respective derivative atany one of the predetermined points exceeds a respective predeterminedthreshold for the derivative at said one predetermined point.
 10. Methodaccording to claim 7, wherein the deep fryer is configured for the deepfrying of potatoes.
 11. A control for automatically switching off powerto a heating element of a deep fryer when the heating element is notimmersed in oil in the deep fryer, the deep fryer comprising a vesselhaving a closed bottom and sides wherein the heating element extendssubstantially horizontally within the vessel for direct contact with theoil, the control comprising at least one temperature sensor forcontinuously measuring temperature at least one predetermined point onthe heating element, a differentiator determining a derivative of thecontinuously measured temperature and a comparator comparing thederivative with a predetermined threshold and terminating power to theheating element when the derivative exceeds a predetermined threshold.12. Control according to claim 11, wherein the deep fryer is configuredfor deep frying or potatoes.